Fuel injection valve

ABSTRACT

The invention provides an electromagnetic driven type fuel injection valve employing an electromagnetic coil spring for a valve closing spring, which can achieve an accurate valve function over a long period of time while making interference between members caused by the valve closing spring to the minimum. In an electromagnetically driven type fuel injection valve in which a stopper core is arranged so as to be fitted and inserted in a through hole of an electromagnetic coil case, a plunger slidably arranged on the same center line as the stopper core has a needle insertion hole pierced from the proximal end surface, a leading end portion of a needle is inserted in the needle insertion hole, and an electromagnetic coil-shaped valve closing spring arranged in compression and having proximal end side wound around an approximately columnar spring retaining portion provided in a protruding manner on the needle leading end surface urges the plunger so that the valve closing spring closes the valve when the electromagnetic coil is not excited, and attracts the plunger to the stopper core so as to open the valve when the electromagnetic coil is excited. The valve closing spring has a proximal end portion which is not elastically deformed and a center portion which is elastically deformed, the proximal end portion having a diameter smaller than that of the center portion, the proximal end portion being wound around the spring retaining portion in close contact therewith has a proximal end portion which is not elastically deformed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetically driven typeinjection valve (injector) which controls a fuel supplied to an engineon the basis of an electric signal transmitted from an electroniccontrol unit so as to inject to an intake pipe.

2. Description of Related Art

An electromagnetically driven type fuel injection valve controlled so asto be opened and closed on the basis of an electric signal output froman electronic control unit is described, for example, in JapaneseUnexamined Utility Model Publication No. 55-180066, and is generallyused as a normally closed type structured such that the valve is openedby exciting a stopper core 6 serving as a stationary iron by applying anelectric current to an electromagnetic coil 5 to attract a plunger 10serving as a movable iron core to move backward a needle 7 having avalve structure on a leading end side, and the valve is closed byreturning the plunger 10 on the basis of an urging force of a valveclosing spring 111 by stopping the current application, as shown in FIG.3.

In the electromagnetically driven type fuel injection valve 11 using thevalve closing spring 111 as mentioned above, in addition to a matterthat the valve body is subtly reacted to the electric signal, it isdesirable that an accurate valve function is achieved over a longperiod.

In this case, in the valve employing the electromagnetic coil spring forthe valve closing spring 111 such as the fuel injection valve 11 shownin FIGS. 3 and 4, the valve opening and closing motion is achieved onthe basis of a comparative simple structure, however, in the light ofsecuring an accuracy of the valve function, a valve employing adisc-shaped leaf spring for the valve closing spring is excellent, suchas a fuel injection valve described, for example, in Japanese UnexaminedPatent Publication No. 9-79107 and Japanese Unexamined PatentPublication No. 2004-211563.

In other words, since it is possible to avoid a problem that an outerperipheral portion of a valve closing spring is brought into contactwith and interfered with a peripheral member in addition that a movablecore and a valve body reciprocate in a floating state without anyslidable portion, by employing the disc-shaped lead spring arrangedperpendicularly to the reciprocating motion of the movable core, it ispossible to limit the reduction of the accuracy of the valve functioncaused by a motion inhibition of the movable core and an abrasion of themember to the minimum.

However, in the fuel injection valve using the disc-shaped leaf spring,in addition that a predetermined magnitude (diameter) is necessary inthe leaf spring for securing a predetermined valve stroke, whereby acertain level of outer diameter (horizontal width) of the fuel injectionvalve is necessary, the structure becomes slightly complicated and acost increase tends to be generated. Accordingly, in addition to thetechnique using the disc-shaped leaf spring, there has been desired adevelopment of a technique which can easily achieve an accuracy of thevalve function over a long period even in the valve employing theelectromagnetic coil spring.

SUMMARY OF THE INVENTION

The present invention is made to solve the problems mentioned above, andan object of the present invention is to provide an electromagneticdriven type fuel injection valve employing an electromagnetic coilspring for a valve closing spring, which can achieve an accurate valvefunction over a long period while making an interference between memberscaused by the valve closing spring to the minimum.

Accordingly, in accordance with the present invention, there is providedan electromagnetically driven type fuel injection valve comprising: anelectromagnetic coil case having a through hole; a stopper core servingas a stationary core fitted in the through hole of the electromagneticcoil case; a plunger serving as a movable core slidably arranged on aleading end side of the stopper core on a center axis thereof coaxialwith an axis of the stopper core, the plunger having a needle insertionhole pierced from a proximal end surface thereof in a leading enddirection at a predetermined depth; a needle extending from the leadingend side of the stopper core and inserted at its leading end portion inthe needle insertion hole, the needle having a leading end surface andan approximately columnar spring retaining portion extending from theleading end surface and having a diameter smaller than that of theneedle; and an electromagnetic coil-shaped valve closing spring arrangedaround the spring retaining portion on its proximal end side incompression in a depth direction of the insertion hole, for urging theplunger in the leading end direction so that the valve closing springcloses the valve when an electromagnetic coil is not excited, andattracts the plunger to the stopper core to open the valve when theelectromagnetic coil is excited; wherein the valve closing spring has aproximal end portion which is not elastically deformed and a centerportion which is elastically deformed, the proximal end portion having adiameter smaller than that of the center portion, the proximal endportion being wound around the spring retaining portion in close contacttherewith.

As mentioned above, since the proximal end portion of the valve closingspring is closely wound around and in close contact with the springretaining portion of the needle, and the winding diameter is madesmaller than that of the center portion, it is possible to limit theinterference with the inner peripheral surface of the insertion hole tothe minimum, and it is possible to achieve an accurate valve functionover a long period, while the outer peripheral side of the proximal endportion of the valve closing spring is interfered with the innerperipheral surface of the insertion hole so as to prevent the smoothvalve motion at a time when the plunger slides and the durability tendsto be lowered due to the abrasion, in the conventionalelectromagnetically driven type fuel injection valve in which the valveclosing spring is interposed within the plunger insertion hole.

Further, in the fuel injection valve, if it is arranged such that thediameter of the proximal end portion of the valve closing spring issmaller than that of the needle, so that at least the outer peripheralside of the proximal end portion of the valve closing spring does notcontact the inner peripheral surface of the plunger insertion hole, thesliding motion of the plunger becomes smoother, and it is possible tomake the valve function further accurate.

Further, in the fuel injection valve mentioned above, if it is arrangedsuch that the needle is provided with a predetermined position adjustingmeans in the proximal end side so as to be capable of changing theinsertion depth so that a valve pressure by the valve closing spring isadjustable, it is possible to easily respond to a change of the valvepressure due to various reasons.

In accordance with the present invention in which the proximal endportion of the valve closing spring arranged in the plunger insertionhole is made smaller in diameter than that of the center portion, it ispossible to limit the interference between the members by the valveclosing spring to the minimum, and it is possible to achieve an accuratevalve function over a long period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view showing an embodiment inaccordance with the present invention;

FIG. 2 is an enlarged view of a main portion in FIG. 1;

FIG. 3 is a longitudinal cross sectional view showing a prior art; and

FIG. 4 is an enlarged view of a main portion in FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

The description will be given of a best mode for carrying out thepresent invention with reference to the accompanying drawings. In thiscase, in the present invention, a portion of a valve closing springwhich is not elastically deformed means a portion in which anelectromagnetic coil-shaped spring is wound at an angle (in anapproximately circumferential direction) at which the spring cannot becompressed in a lengthwise direction (a direction of a center line), anda portion of the valve closing spring which is elastically deformedmeans a portion in which the coil-shaped spring is wound at an angle atwhich the spring can be compressed in the lengthwise direction.

FIG. 1 shows a longitudinal cross sectional view of a fuel injectionvalve 1 in accordance with the present embodiment. The fuel injectionvalve 1 is formed by fitting and inserting an end cover 3 in a proximalend side of a case main body 2 provided with an injection portion inwhich an outer case is formed in a cylindrical shape and an injectionhole 9 is provided in a leading end side. Further, an electromagneticcoil case 4 retaining an electromagnetic coil 5 and having a pair ofconducting terminals 41 and 41 mounted on the proximal end side iscoaxially provided within the outer case.

The electromagnetic coil case 4 is structured such that a through hole42 is pierced in conformity to a center line, and a tubular stopper core6 is arranged so as to be fitted and inserted in the through hole 42.The stopper core 6 is constituted by a magnetic body, and serves as-astationary core excited by applying an electric current to theelectromagnetic coil 5. Further, a rod-like needle 7 is arranged so asto pass through a through hole 61 provided in such a manner as to passthrough the stopper core 6 along the center line thereof, from theproximal end side to the leading end side.

The needle 7 extends from the leading end surface of an approximatelycolumnar adjusting member 73 arranged so as to be fitted and inserted ina retaining hole 44 of a tubular retaining member 43 fixed to theelectromagnetic coil case 4 in the proximal end side of the stopper core6, has a spring retaining portion 81 formed in a columnar shape on theend surface of the leading end portion protruding from the leading endsurface of the stopper core 6 and having a diameter smaller than that ofthe needle 7, so that an insertion depth of the needle 7 can be changedso as to adjust a valve pressure by a valve closing spring 101, byoperating the adjusting member 73 in the retaining hole 44 from anopening portion so as to change a position on the center line.

An approximately columnar plunger 10 constituted by a magnetic body isarranged on a leading end side of the stopper core 6 so as to beslidable on the leading end side of the through hole 42 of theelectromagnetic coil case 4 and on the center line of the stopper core6, and a leading end portion thereof protrudes from the leading endsurface of the electromagnetic coil case 4 so as to form a valvestructure portion 72 in the leading end. Further, a needle insertionhole 71 is pierced at a diameter capable of inserting the needle 7 fromthe proximal end surface of the plunger 10 toward the leading end, andthe electromagnetic coil-shaped valve closing spring 10 is provided in aspring retaining portion 81 provided in a protruding manner on theleading end surface of the needle 7 inserted in the needle insertionhole 71, is interposed in a compressed state in the depth direction ofthe needle insertion hole 71 between the bottom surface of the needleinsertion hole 71 and the leading end surface of the needle 7, andpresses the plunger 10 toward the leading end so as to energize thevalve structure portion 72 in the valve closing direction.

Here, the structure mentioned above, and the valve function of closingthe valve on the basis of the energizing force of the valve closingspring 101 when the electromagnetic coil 5 is not excited, and openingthe valve by attracting the plunger 10 against the urging force of thevalve closing spring 101 on the basis of the excitation of the stoppercore 6 when the electromagnetic coil 5 is excited, are already wellknown techniques.

Further, the present invention has a feature in the structures of thespring retaining portion 81 arranged in the leading end side of theneedle 7 inserted into the needle insertion hole 71 of the plunger 10,and the valve closing spring 101 held thereto, as shown in FIG. 2 whichcorresponds to the enlarged partial view of FIG. 1.

In other words, as shown in FIG. 4 which corresponds to an enlargedpartial view of the fuel injection valve 11 shown in FIG. 3, thestructure for urging the plunger 10 in the conventional fuel injectionvalve in the valve closing direction is made such that the valve closingspring 111 interposed in the compressed state in the leading end side ofthe needle 7 inserted into the needle insertion hole 71 so as to befixed at its position has the same winding diameter from the proximalend portion 112 through the center portion 113 to the leading endportion, and the proximal end portion 112 corresponding to the fixedportion which is not elastically deformed has approximately the sameouter diameter as the outer diameter of the needle 7. Accordingly, thereis a problem that the proximal end portion 112 is interfered with theinner peripheral surface of the needle insertion hole 71 when theplunger 10 slides, and obstructs the smooth motion of the plunger 10,and it is hard to secure an accuracy of the valve function. Therefore,the problem mentioned above is solved by the present invention havingthe structure mentioned below.

As shown in FIG. 2 corresponding to the enlarged partial view of FIG. 1,the structure is made such that the spring retaining portion 81 in theleading end side of the needle 7 is made slightly smaller than theconventional one, and regarding spring retaining portion 81 arrangedtherearound, the proximal end portion 103 which is not elasticallydeformed is wound around the proximal end side outer peripheral surfaceof the spring retaining portion 81 in close contact therewith, and theelastically deformed center portion 104 has the larger diameter than theproximal end portion.

In accordance with the structure mentioned above, the outer peripheralside of the proximal end portion of the valve closing spring 111, whichmight be conventionally interfered with the inner peripheral surface ofthe needle insertion hole 71 so as to generate the trouble, is notabsolutely brought into contact with the inner peripheral surface of theneedle insertion hole 71 over the time from a standstill time to asliding time, and it is possible to smoothly maintain the sliding motionof the plunger 10 so as to easily secure the accurate valve function.Further, since the friction is hard to be generated by the interferencebetween the members, it is possible to avoid the reduction of thedurability due to the abrasion.

In this case, since the valve closing spring 101 does not meander withinthe needle insertion hole 71 by making the outer diameter of theelastically deformed center portion 104 of the valve closing spring 101approximately identical to the outer diameter of the needle 7, it ispossible to stably achieve the urging force. Further, the adjustment inthe depth direction of the needle 7 by the adjusting member 73 may beexecuted by turning the adjusting member 73 having a screw head formedin the proximal end side from the outer portion by a driver or the likein such a manner as to screw a thread ridge provided on an outerperipheral surface of the adjusting member 73 into the retaining hole 44of the retaining member 43 having a thread groove, or the adjustingmember 73 may be appropriately moved by setting an O-ring 45corresponding to a seal member provided in the adjusting member 73 so asto serve as the stopper member, and applying a pressure equal to or morethan a predetermined level from the outer portion.

1. An electromagnetically driven type fuel injection valve comprising:an electromagnetic coil case having a through hole; a stopper coreserving as a stationary core fitted in the through hole of theelectromagnetic coil case; a plunger serving as a movable core slidablyarranged on a leading end side of the stopper core on a center axisthereof coaxial with an axis of the stopper core, the plunger having aneedle insertion hole pierced from a proximal end surface thereof in aleading end direction at a predetermined depth; a needle extending fromthe leading end side of the stopper core and inserted at its leading endportion in the needle insertion hole, the needle having a leading endsurface and an approximately columnar spring retaining portion extendingfrom the leading end surface and having a diameter smaller than that ofthe needle; and an electromagnetic coil-shaped valve closing springarranged around the spring retaining portion on its proximal end side incompression in a depth direction of the insertion hole, for urging theplunger in the leading end direction so that the valve closing springcloses the valve when an electromagnetic coil is not excited, andattracts the plunger to the stopper core to open the valve when theelectromagnetic coil is excited; wherein the valve closing spring has aproximal end portion which is not elastically deformed and a centerportion which is elastically deformed, the proximal end portion having adiameter smaller than that of the center portion, the proximal endportion being wound around the spring retaining portion in close contacttherewith.
 2. The fuel injection valve as claimed in claim 1, whereinthe diameter of the proximal end portion of the valve closing spring issmaller than that of the needle, so that at least the outer peripheralside of the proximal end portion of the valve closing spring does notcontact the inner peripheral surface of the plunger insertion hole. 3.The fuel injection valve as claimed in claim 1, wherein the needle has apredetermined position adjusting means in the proximal end side so as tobe capable of changing the insertion depth so that a valve pressure bythe valve closing spring is adjustable.
 4. The fuel injection valve asclaimed in claim 2, wherein the needle has a predetermined positionadjusting means in the proximal end side so as to be capable of changingthe insertion depth so that a valve pressure by the valve closing springis adjustable.